An Open-label, Phase I Dose Escalation and Phase 2 Dose Expansion Study to Assess Safety, Tolerability, Preliminary Antitumor Activity of SMP 3124LP in Adults with Advanced Solid Tumors

The goal of this clinical trial is to evaluate the safety and efficacy of TOS-358 in women with HR+ HER2- metastatic breast cancer whose tumors have a mutation in PIK3CA and who meet all other study enrollment criteria. The main questions it aims to answer are:

1. Phase 1a: what is the maximum tolerated dose and recommended dose for phase 2?
2. Phase 1a: how safe and tolerable is TOS-358 at different dose levels when taken orally once or twice per day?
3. Phase 1b: how safe and effective is TOS-358 when given with standard of care medicines for HR+HER2- metastatic breast cancer (fulvestrant and CDK4/6i)

The purpose of this study is to determine if the radiotracer, \[68Ga\]Ga-ABY-025, used for PET imaging can help us better identify and visualize lesions or tumors, in patients who are receiving standard of care therapy HER2+ cancers.